Although I am not in a position to comment on the politics and/or technical reasons for percentage limitation for feeding solar-generated energy into the electrical grid, I want to suggest that your readers consider an alternative to feeding solar-generated power into the grid or batteries. That alternative is breaking down water into hydrogen and oxygen.
I learned about this alternative at the Solar House competition sponsored by the Department of Energy at the National Mall in Washington, D.C. In this competition, teams from colleges and universities submit complete, functioning designs for 400-square-foot solar houses.
In what I believe was the 2008 competition, the design from the New York Institute of Technology used their solar array to hydrolyze water into storable tanks of hydrogen and oxygen, which were then used to power a fuel cell manufactured by the Plug Power Corporation.
At this time, fuel cells are, in fact, rather expensive, but this approach holds some particular advantages. For example, in the Arctic, the approach allows for a year-round supply of sustainable energy (to include the complete darkness of winter).
Perhaps this is why the U.S. Department of Defense has carried out extensive testing of residential fuel cells through the Army Construction Engineering Research Laboratory in Champaign, Ill.
In addition, residential fuel cells are immune to disruption of the grid by earthquake, hurricanes and terrorist attacks.